In Reply We thank Liu et al for their interest in our study. We herein address their comments. First, they discuss how we do not show temporality, one of the Hill causality criteria,1 that is, exposure precedes outcome. While our home monitoring occurred after the clinical examination, we believe it represented participants’ exposure even prior to their clinical examination as our longitudinal data indicate relative stability of indoor air pollution in an individual’s home.2 As of December 20, 2020, 39 sensors were operational in the participants’ homes, continuously monitoring both gaseous and particulate matter (PM) pollutants every 5 minutes. From June to December 2020, the concentration of weekly interhousehold average particulate matter of 2.5 μm or less (PM2.5) was 6.5 μg/m3, with a range of 1.4 μg/m3 to 30.2 μg/m3. Intrahousehold 1-week lagged variation (ie, the difference between household-specific weekly PM2.5 average and its corresponding level a week prior) was 0.31 μg/m3 (ie, less than 5% of the weekly average). This suggests greater interhousehold weekly variation than intrahousehold weekly variation in PM2.5. Furthermore, short-term temporality is important for acute-effect studies, such as asthma exacerbation that requires short-term exposure prior to the exacerbation. However, participants with dry eye disease symptoms had a history of chronic symptoms.
Galor A, Kumar N. Association of the Indoor Environment With Dry Eye Metrics—Some Additional Evidence to Pursue—Reply. JAMA Ophthalmol. 2021;139(7):812. doi:10.1001/jamaophthalmol.2021.1597
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